Coded labels



United States Patent 3,521,280 CODED LABELS Maurice Janco, Arnold T. Nordsieck, and Charles W. Perkins, Santa Barbara, Calif., assignor to General Research Corporation, Santa Barbara, Calif., a corporation of California Filed Jan. 16, 1969, Ser. No. 791,676 Int. Cl. G01s 9/56 US. Cl. 343-65 Claims ABSTRACT OF THE DISCLOSURE A system of coding objects such as packages or vehicles with identification, routing and other information. A label suitable for application directly on the object or by means of an adhesive sticker or the like. A microwave system with a. label in the form of a plurality of resonators of different resonant frequencies. The presence or absence of a resonator for a particular frequency provides a bit of information. A resonator may be physically present but inactivated by punching out or burning out a portion of it and thus make it effectively absent. A transmitter for producing an output having the frequencies of the various resonators and a receiver for operation over the range of the resonant frequencies, with the receiver providing an output when the receiver input signal differs substantially from the background signal, as when a particular resonator is being excited by energy of its resonant frequency. A variable frequency transmitter with the output frequency being swept over the range of the resonant frequencies of the resonators.

This invention relates to systems for identifying objects and to new and improved labeling devices and label reading equipment. There is a need for a small and cheap form of label and an accurate and fast label reading mechanism not requiring precise placement of the label with respect to the reading apparatus. A typical application of such a system is in the control of inventory in a store. A coded label can be applied to each item at the time it enters the store or warehouse or at the time it is manufactured and the label can remain on the item until it is sold or delivered or consumed. The label may be coded to provide identification of the object and other information as desired, such as serial number, a routing, a price, a date, and the like. The label may be read at any time to obtain the coded information which in turn can be used for a variety of purposes. In one example, a quantity of information can be stored in a computer with the label code being related to the stored information. Reading of the label, as when the object passes a selling point or a check-out point, provides object identification to the computer for any desired use. One typical example could be the counting and classification of all of the objects for inventory purposes.

Other applications of the system include freight and baggage handling at airline and truck terminals, book handling in libraries, routing of mail and baggage, and the like. It is readily realized that any type of information may be coded in the label and the information as read from the label can be used for a wide variety of purposes.

A practical labeling system should be operable without requiring physical orientation or positioning of the object and without manual intervention and without requiring physical contact with the labeled object. The label itself must be quite cheap because many of them will be utilized. The possibility of error in reading must be very low. The system should operate over extremes of temperature and humidity, in high sound levels and in high dust and dirt environments.

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The presently suggested systems have not met these requirements. Optical systems do not require contact with the object, but usually require precise registration and are susceptible to failures because of dirt, stray light and other environmental conditions. Some microwave systems have been suggested but relatively expensive labels are required.

The present invention utilizes microwave techniques with a simple cheap label construction. Information is coded in frequency using high-Q resonant structures in the label, with the label being scanned in frequency by a transmitter with frequencies corresponding to the resonant frequencies of the resonant structures in the label. The resonant structures or resonators of the label are passive and small in size, they are readily fabricated by metal deposition on plastic and will provide a large number of bits of information in a small physical size. A variety of label forms and manufacturing techniques are available.

It is a general object of the invention to provide such a new and improved labeling system which overcomes the disadvantages of the prior art systems. A particular object is to provide coded labels for a labeling system with each coded label including a plurality of resonators of different resonant frequencies, with the presence or absence of a resonator of a particular frequency providing a bit of information. An additional object is to provide a transmitter and receiver for reading the information carried by a label, with the transmitter output of a particular frequency being reflected to the receiver with a change in amplitude and/ or phase as a function of the presence or absence of a resonator for such frequency.

Other objects, advantages, features and results will more fully appear in the course of the following description. The drawings merely show and the description merely describes preferred embodiments of the present invention which are given by way of illustration or example.

In the drawings:

FIG. 1 is a plan view of a label incorporating the preferred embodiment of the invention;

FIG. 2 is a sectional view taken along the line 22 of FIG. 1;

FIGS. 3 and 4 illustrate alternative configurations for the conducting strip of the label of FIG. 1;

FIG. 5 is a plan view of an alternative form of label;

FIG. 6 is a sectional view taken along the line 6-6 of FIG. 5;

FIG. 7 is a plan view of another alternative form of the label;

FIG. 8 is a sectional view taken along the line 88 of FIG. 7; and

FIG. 9 is a block diagram of an overall system incorporating the preferred embodiment of the invention.

Referring to FIGS. 1 and 2, the label includes a dielectric layer or sheet 20, typically of plastic, with a conduct ing layer 21 on the back of the dielectric layer. An adhesive film 22 may be applied to the conducting layer 21 for afiixing the label to an object. A conventional peelable backing sheet 23 may be applied over the adhesive layer for protection.

A plurality of conducting strips 25 is carried on the face of the dielectric layer 20, with each strip connected at one end to the conducting layer 21, as illustrated in FIG. '2.

Each of the conducting strips 25 is a different length and the length is selected to be equal to a quarter wave length of a predetermined frequency, so that each strip forms a quarter wave resonant structure or resonator.

By way of example, for X-band frequencies, the conducting layer 21 need be only a few skin depths thick, say 50 micro-inches of copper, and can be foil or an electroplated layer or a spray-deposited layer. The dielectric layer 20 may be a moderately flexible plastic about .030 inch thick. The conducting strips 25 may be straight strips of copper 50 micro-inches thick, 0.01 inch wide and of length equal to a quarter wave length at the resonant frequency of the particular strip. If the dielectric constant of the plastic is about 2, the average length of the strips at X- band frequencies is about 0.21 inch. Each resonator requires an area of about 30 square inch, permitting about 50 resonators per square inch of label. Neighboring resonators will couple appreciably if they have neighboring resonant frequencies, but this does not present a problem since the location of a resonator on the label has no significance. Hence the distribution of resonators of different resonant frequencies over the surface of the label can be chosen to minimize coupling.

Information is coded into a label by omitting or inactivating particular conducting strips, i.e., particular resonant frequencies. This could be accomplished by manufacturing each label with particular conducting strips, but it appears to be far simpler to manufacture all labels with all conducting strips and then inactivate selective resonators, as by selective burn-out or punching, leaving openings 26 in the label. This provides a ready form of binary coding for the information carried by a label. The resonators can be selectively burned out by using a transmitter similar to the transmitter portion of the microwave system shown in FIG. 9. By raising the output power level of the transmitter to a critical point in a narrow frequency band the resonant conducting strip can be made to absorb enough energy to melt. A coppper strip 50 micro-inches thick, 0.1 inch wide can be melted by a few watts of power. Thus a label can be coded by transmitting sufiicient energy at the frequencies to be eliminated.

A protective coating may be applied over the face of the label to provide mechanical protection for the conducting strips 25. Polystyrene is a typical coating material. These surfaces may have the ability to accept written or printed information. In the sectional view of FIG. 2, the thickness of the various layers is greatly exaggerated for illustrative purposes. A typical label would be in the order of .030 to .050 inch thick.

While the presently preferred configuration for the resonators is the straight strip as illustrated in FIG. 1, other configurations may be utilized and a serpentine configuration is illustrated in FIG. 3 and a spiral configuration is illustrated in FIG. 4.

The coded label is aflixed to the object to be identified. The label is read by irradiating the label from a transmitter with output frequencies corresponding to each of the possible resonant frequencies of the resonators. A receiver picks up energy reflected from the label and from background objects. When the transmitter radiates a frequency for which there is a resonator active on the label, there will be a change in the signal at the receiver. This may be a change in amplitude or in phase or both. There may be an increase in amplitude or a decrease in amplitude, depending upon whether the wave scattered back by the resonator is in or out of phase at the receiver with the wave scattered by the background. Similarly, there may be a change in phase if the Wave scattered back by the resonator is in quadrature with the background wave at the receiver. The response of the label to each of the possible resonant frequencies is determined and recorded, providing a binary output corresponding to the information coded into the label.

An alternative form for the label is illustrated in FIGS. 5 and 6. A plurality of conducting strips 30 of various lengths is applied to a dielectric layer 31. As in the embodiment of FIGS. 1 and 2, the lengths of the conducting strips are selected to provide resonance at particular frequencies. Selected resonators 30 can be applied to the layer 31, or resonators corresponding to all possible frequencies can be applied and then selected resonators can be spoiled or removed to provide the coding. The dielectric layer 31 may be designed for application to the object by means of an adhesive coating similar to that of 4 FIGS. 1 and 2. Alternatively, the resonators 30* can be applied directly to a dielectric portion of the object.

Another alternative form of the label is illustrated in FIGS. 7 and 8. A conducting layer 34 is applied over a dielectric layer 35. A plurality of openings 36 of various lengths is provided in the conducting layer 34, with each opening 36 serving as a resonator. In one method of production, the desired openings 36 may be made in the conducting layer 34 prior to or at the time of its application to the dielectric layer 35. Alternatively, a continuous conducting layer may be applied on the dielectric layer and the openings 36 may be formed through both openings, as by punching. The label may be applied to the object with the dielectric layer or the conducting layer 34 exposed. Alternatively, the conducting layer 34 may be applied directly to a dielectric portion of the object to be identified.

An alternative form of the configuration shown in FIG. 1 is half-wave strips of conductor shorted to the backing conducting sheet at both ends. However, this alternative appears to have no advantage over the one shown. It does have the disadvantage of requiring twice the label area per resonator. The configuration of FIG. 1 has the important advantage, compared to those of FIG. 5 and FIG. 7, in that it may be attached to a metal surface without appreciably detuning the resonators since it incorporates a metallic shield within itself.

The labeling system includes a transmitter which sends microwave energy toward the object with the label thereon. The transmitter output includes the frequencies to which the resonators are tuned. The microwave energy reflected by the label and the objects around it is received by a receiver. The characteristics of the received energy determine which of the possible resonators are present in the particular label and which are not. The characteristics of the received energy may include an increase or decrease in amplitude and/ or a shift in phase. The receiver includes a detector which determines whether or not there is a change in characteristic for each possible resonant frequency and produces a binary output suitable for recording or transmission by conventional binary digital data handling equipment.

Various transmitter and receiver configurations may be utilized. The transmitter output may be continuous or pulsed. The transmitter output may be wide band or it may be swept across the range of possible resonant frequencies. Similarly, the receiver may be wide band or may be swept across the possible resonance frequencies. Of course, both transmitter and receiver cannot be wide band in the same system because this precludes distinguishing among the various resonant frequencies. If both transmitter and receiver are being swept, they must be operated in synchronism. A preferred form of swept transmitter and receiver combination is illustrated in FIG. 9.

Referring to FIG. 9, a plurality of boxes 50, each with a coded label 51, moves past an interrogation station on a conveyor belt 52. A transmitter antenna 53 directs a transmitter output to each label as the box passes the station. A receiver antenna 54 picks up reflected energy from the label and the box.

In the preferred embodiment illustrated, the transmitter includes a frequency modulatable transmitter 55 operating in the range of 10 gHz. and a sawtooth signal generator 56, operating at 10 kI-Iz., providing a control signal on line 57 for sweeping the output frequency of the transmitter 55. The transmitter output is coupled to the antenna by a line 58.

In the preferred embodiment illustrated in FIG. 9, the receiving system utilizes two heterodyne receivers 60, 61 for reducing cluttenfThe receiver 60 is a relatively wide band receiver and has a relatively short time constant. Typically, the pass band could be 10 mHz. and the time constant .03 microsecond. The receiver 61 is a relatively narrow band receiver with a relatively long time constant.

Typically, the pass band could be .1 mHz. and the time constant 3 microseconds. The antenna 54 is connected to the input of each receiver by a line 62. The output of the transmitter 55 is coupled to a single side band modulator 65 by line 66. The output of an intermediate frequency oscillator 67 is coupled to the modulator 65 by a line 68. For the specific example being described, the oscillator may operate at 30 mHz. The output of the modulator 65 is connected to each of the receivers 60, 61 by line 69 and provides the variable frequency signals for sweeping the receiver pass bands in synchronism with the transmitter output frequency. The signal on line 69 is the IF, or intermediate frequency. It differs at all times from the transmitted and received frequency by 30 mHz. Therefore, when it is mixed with the received signal the result will include a signal of 30 mHz. This signal is then fed to the differential amplifier. Since the transmitted signal, which is swept through its range at a kHz. rate, is fed into the single side band modulator, the IF will also be swept through its range at the same rate in synchronism.

The outputs of the receivers 60, 61 are connected to a differential amplifier 72 by lines 73, 74. The differential amplifier subtracts the vector voltages from the receivers, providing a difference signal on line 75 to a detector 76. The detector output is connected to a pulse reshaper 77, which in turn may be connected to a binary register 78. A typical detector output is illustrated at 79 and a typical pulse reshaper output is illustrated at 80.

As the frequency of the transmitter and the pass bands of the receivers sweep in synchronism, the receivers will see a signal due to clutter and, when a change in signal returns from a resonator, the receivers will see a rapid change in amplitude and/or phase. The receiver 60 with the short time constant responds to the signal from the resonator and to the clutter. The receiver 61 with the longer time constant responds to the clutter signal, but its response to the resonator signal is very low. The two clutter signals tend to cancel each other in the differential amplifier, leaving an enhanced resonator signal for subsequent detection, shaping and other manipulation.

Since the time required for a single sweep across the entire frequency band is usually less than the time the label will be in View, the system can be operated to execute a number of scans for each label. The sawtooth generator output may also be connected to the binary register via a line 82 to provide a signal for transmitting the stored information from the register 78 at the end of each sweep. The results of multiple scans of the same label can be processed to check errors and obtain most likely label message.

A specific example of a label was set out above. The resonators of such a label will have a Q of 200 or higher. Further considering this specific example, the operating frequency of the transmitter can be centered about 10 gHz., with a band width for each resonator of 50 mHz. The resonant frequencies of the resonators can be spaced a band width apart and a system utilizing 50 resonators per label, or 50 bits in the code, will have a band width requirement of 5 gHz. The transmitter can then operate over the range of 7.5 gHz. to 12.5 gHz. The instantaneous band width of the narrow band receiver may be 0.1 mHz. and that of the wide band receiver may be 10 mHz.

With such a system, the range of the resonant frequencies may be swept in .5 microsecond, requiring a sawtooth generator frequency of 20 kHz. A lower frequency such as 10 kHz. or 5 kHz. would be adequate for many applications. Assuming that the object with the label is moving at ten miles per hour horizontally and the antennas are spaced three meters from the object with a 6" horizontal field of view, a sweep rate of 5 kHz. would give 300 sweeps during the time the label is in the field of view. It is estimated that a system operating at 10 gHz. with a 50 mHz. band width for the resonators and a 3 meter spacing between antennae and label, the transmitter power requirement would be less than A watt. From these figures it is readily seen that the operating requirements for the labeling system are well within the range of present day technology.

We claim:

1. In a labeling system for identifying objects, the combination of:

a plurality of microwave resonators of different resonant frequencies for attaching to an object to be identified, each of said resonators comprising strips of electrical conducting material of different lengths on one side of a layer of dielectric material and a layer of electrical conducting material on the other side of said dielectric material, with said strips connected to said electrical conducting layer through said dielectric layer;

a transmitter for producing an output having the frequencies of said resonant frequencies;

first antenna means for directing said transmitter output toward said resonators;

a receiver for operation over the range of said resonant frequencies and including means for generating an output signal when the received signal differs substantially from the background signal; and

second antenna means directed toward said resonators for picking up an input for said receiver.

2. A coded label for an object for radiation by a microwave transmitter for reflecting energy toa receiver for identifying the object and comprising a plurality of resonators of different resonant frequencies for attaching to the object, each of said resonators comprising strips of electrical conducting material of different lengths on one side of a layer of dielectric material and a layer of electrical conducting material on the other side of said dielectric material, with said strips connected to said conducting layer through said dielectric layer.

3. In a labeling system including a plurality of micro wave resonators of different resonant frequencies attached to an object to be identified, the combination of:

a transmitter for producing an output varying in frequency over the range of resonant frequencies of the resonators, said transmitter including a control signal generator for repeatedly sweeping the transmitter output across said frequency range;

first antenna means for directing said transmitter output toward the resonators on the object;

a receiver for operation over the range of the resonant frequencies and for generating an output signal when the receiver input signal differs substantially from the background signal, said receiver including a first receiver with a variable and relatively wide pass band;

a second receiver with a variable and relatively narrow pass band;

means for combining the outputs of said first and sec ond receivers to provide a difference signal;

second antenna means directed toward the object with the resonators for picking up an input for said receiver;

a local oscillator; and

modulator means for combining the transmitter output and the local oscillator output to provide a band pass frequency control for said first and second receivers for varying the frequency of said pass bands in synchronism with the frequency of the output of said transmitter.

4. In a labeling system for identifying objects, the

combination of:

a plurality of microwave resonators of different resonant frequencies for attaching to an object to be identified;

a transmitter for producing an output having the frequencies of said resonant frequencies, said transmitter including means for varying the output frequency thereof over the range of said resonant frequencies;

first antenna means for directing said transmitter output toward said resonators;

a receiver for operation over the range of said resonant frequencies and for generating an output signal when the received signal differs substantially from the background signal;

second antenna means directed toward said resonators for picking up an input for said receiver;

said receiver including a first receiver with a variable and relatively wide pass band;

a second receiver with a variable and relatively narrow pass band;

means for connecting said second antenna means as an input to each of said first and second receivers;

means for combining the outputs of saidfirst and second receivers to produce a difference signal; and

means for varying the frequency of said pass bands in synchronism with the frequency of the output of said transmitter.

5; A system as defined in claim 4 in which said first receiver has a relatively short time constant and said second receiver has a relatively long time constant.

References Cited UNITED STATES PATENTS RODNEY D. BENNETT, 1a., Primary Examiner M. F. HUBLER, Assistant Examiner Us. c1.- X.R. 

